1. Field of the Invention
The invention relates to a pneumatic-hydraulic blind riveting device with a pulling device arranged in a device housing and comprising a chuck housing that is connected with a hydraulic pulling piston and surrounds chuck jaws against which a pressure bushing arrangement rests which cooperates with a return piston.
2. Description of the Related Art
Such a blind riveting device is known from German patent DE 31 53 057 C2. The energy required for the riveting action of a blind riveting device is provided by means of compressed air which is available in many manufacturing facilities at a standard pressure of 6 bar. This compressed air actuates a pneumatic piston. This pneumatic piston is rigidly connected to a hydraulic piston which has a considerably smaller active surface. The hydraulic piston generates accordingly a relatively high pressure in a hydraulic liquid. This hydraulic liquid acts then onto the pulling piston. The pulling piston has a pulling force-transmitting connection with the chuck housing. The chuck housing has at its inner side a conically extending contact surface for the chuck jaws which rest in a ready position of the riveting device on a mouth and can thus be inserted into the chuck housing so that they open and a riveting drift of a blind rivet can be inserted. The movement of the chuck housing caused by the pulling piston has two effects. On the one hand, the chuck jaws are pressed together radially inwardly when the chuck housing is moved in the pulling direction across the chuck jaws. When the chuck jaws then secure the drift of the rivet, a further pulling movement of the chuck housing causes the chuck jaws to entrain the drift of the rivet so that the drift initially deforms the hollow rivet in a manner known in the art and subsequently is broken off.
After the drift has broken off, the pneumatic cylinder is relieved so that the hydraulic pressure on the pulling piston decreases. Pressure, for example, resulting from compressed air, now acts on the return piston. The return piston moves the pulling piston and thus also the chuck housing again into the initial position. The pressure bushing arrangement comprises for this purpose at its center a pressure spring so that the return piston can move the chuck housing farther by a small distance when the chuck jaws rests against a mouth of the housing. Accordingly, the chuck jaws become free of the chuck housing and can open. The broken-off riveting drift can then be removed or can be sucked out to the rear of the blind riveting device. A new blind rivet can then be inserted with its riveting drift. In the end, during opening of the chuck jaws the spring, which is responsible for the closing force of the chuck jaws onto the riveting drift during the next riveting process of the blind rivet, is pretensioned.
Such an embodiment of a blind riveting device has basically proven successful in practice. However, after riveting a certain number of blind rivets it was found that the chuck jaws no longer are secured with the desired reliability on the riveting drift. Increasingly, the chuck jaws slide on the riveting drift so that the formation of the rivet connection to be formed with the blind rivet no longer provides the desired reliability. This is so increasingly when the teeth of the chuck jaws are already slightly dull as a result of wear. Accordingly, gripping of the riveting drift is no longer possible or is at least made significantly more difficult; this can result in failure of the device. The chuck jaws then have to be replaced.
It is an object of the present invention to control the riveting process with blind rivets in a reliable fashion.
In accordance with the present invention, this is achieved in that between the return piston and the pulling piston a pressure chamber is arranged which is loadable by means of a control device with a controlled pressure.
With such a configuration it is possible to affect the closing forces acting on the chuck jaws in a more directed way. Primarily, it is possible to effect by means of the controlled pressure an opening of the chuck jaws upon return of the pulling device as well as an application of a closing force which, in general, is greater than the closing force provided by a spring. When the pressure chamber is loaded with pressure, the pulling piston and thus also the chuck housing are moved by the pressure into the front-most position in which the chuck jaws come free of the chuck housing. The chuck jaws, because they rests against the mouth, cannot be moved farther to the front. When however the pressure in the pressure chamber is lowered and at the same time, or at a later point in time, the pulling piston is loaded with hydraulic pressure, the chuck housing-is moved to the rear against the chuck jaws, i.e., away from the mouth, with a force which is as large as the force which secures the return piston in the return piston position. Accordingly, substantially greater forces are transmitted onto the chuck jaws which results in a safe gripping of the riveting drift with a substantially increased service life of the gripping jaws. This primarily reduces the wear of the gripping jaws. At the same time, it can be ensured over a longer period of time that the riveting process for the rivets is carried out with the desired reliability.
Preferably, the pressure bushing arrangement is of a rigid configuration between the return piston and the chuck jaws in the pressure direction. Accordingly, there is no pressure spring arranged between the return piston and the chuck jaws; instead, the return piston can be forced permanently from behind against the chuck jaws. Accordingly, the pressure with which the return piston presses via the pressure bushing arrangement onto the chuck jaws is a measure for the closing force with which the chuck housing can press the chuck jaws together. The closing force, which in the past was supplied by a pressure spring, is thus replaced by a closing force which is controlled by pressures.
Preferably, the pressure bushing arrangement has a pressure bushing which is divided in the transverse direction whose end facing the chuck jaws is embodied as a hollow cylinder with a smooth mantle surface. This part is also a wear member which, if needed, can be easily exchanged. When closing the chuck jaws, there is always a small movement with a corresponding wear at the contact location between the pressure bushing and the chuck jaws because this movement is partially carried out under a relatively high pressure. When now the end of the wear member facing the chuck jaws is formed as an exchangeable part, it is no longer required to exchange the entire pressure bushing arrangement.
Preferably, the control device lowers the pressure in the pressure chamber when it loads the pulling piston in the pulling direction with hydraulic pressure. The change of the two pressures can be carried out simultaneously or at least within a narrow temporal time frame. It is possible in this way to effect the control of the two pressures with a single movement of the hand or finger of the operator. When the pressure in the pressure chamber is lowered, the movement of the pulling piston no longer is counteracted by a direct resistance so that the movement of the pulling piston can be immediately converted into a closing movement with subsequent pulling movement.
Preferably, on both sides of the return piston the same pressure is adjustable, wherein the return piston on a side facing away from the pulling piston has a larger active surface than on a side facing the pulling piston. The adjustment of the same pressures is a relatively simple measure. Required is only a single pressure source. By arranging active surfaces of different sizes at the front side (facing the pulling piston) and the backside of the return piston, it is then possible, also in a very simple way, to apply different forces onto the return piston. These forces are oriented such that the return piston is always loaded in the direction toward the mouth. When the chuck jaws rests against the mouth, only the difference of the two forces acts onto the mouth so that the configuration of the housing must not be excessively greatly dimensioned.
In this connection it is especially preferred that the return piston is connected to a return pipe which projects into a connecting pipe. With the aid of the pulling piston pipe it is now possible in a simple way to reduce the size of the active surface.
Preferably, the side of the return piston facing away from the pulling piston is loaded with a constant pressure. This pressure can be a pressure with which the blind riveting devices operate, for example, compressed air at 6 bar. Since the side of the pulling piston facing away from the return piston must no longer be pressure-controlled, its configuration is very simple. This pressure on the backside of the return piston must only be able to push the pulling device again back into its initial position.
Preferably, the return piston is guided in an ejector pipe. This embodiment has several advantages. On the one hand, on the side of the return piston facing away from the pulling piston a pressure chamber can be formed which is closed to the exterior and at the same time provides a disposal path for broken-off riveting drifts. On the other hand, with an additional guiding of the return piston it is ensured that lateral movements of the return piston are substantially completely excluded so that sealing problems are minimized. It is possible with simple measures to seal the return piston relative to the housing.
In this respect, it is particularly preferred that the ejector pipe comprises a lock which can be actuated by the riveting drift collecting container. The lock has a lock surface which is matched such to the cross-section of the ejector pipe that a gap remains which allows an effective flowing of air but prevents ejection of the blind riveting drifts. This lock is a safety feature. In many blind riveting devices, the broken-off riveting drifts are removed by vacuum or by means of compressed air and are collected in a collecting container. A collecting container not only collects the riveting drifts over a certain period of time. It also prevents that operating personnel is endangered by riveting drifts which, in the truest sense of the word, can be shot out of the pulling mechanism during vacuuming of the device. It is possible to prevent that the riveting drifts are shot out to the rear from the ejector pipe by simply closing off the ejector pipe. However, in this situation, a pressure is generated which in the end leads to the riveting drifts to be shot out toward the front, i.e., through the mouth. These two possibilities are excluded when the lock is now configured such that the air can flow out but the gap between lock and ejector pipe is so small that the riveting drifts can no longer pass through the opening. The riveting drifts remain thus in the ejector pipe as long as the lock is in its locking position. Such a situation occurs, for example, when the operator has removed the collecting container in order to empty it.
In this connection, it is particularly preferred to form the lock by a finger on a plate which is pivotable about an axis which extends parallel to the axis of the ejector pipe. This considerably reduces the construction length of the device. The lock requires practically no space in the axial or pulling direction but can close off reliably the path extending through the ejector pipet
This is true in particular when the finger can be inserted substantially radially into the ejector pipe. In this case, the movement of the lock requires practically no additional construction space.
Preferably, the chuck jaws are guided in the chuck housing in grooves whose groove bottoms have a constant cross-section across a predetermined length, wherein the chuck jaws are matched to their cross-section, respectively. In this case, the chuck jaws are secured in the chuck housing always by a defined pressing surface, independent of the axial position, i.e., the position in the direction of pulling. With this measure, the surface pressing onto the chuck jaws can be maintained identical independent of the position of the chuck jaws. Impermissibly high pressing forces are thus prevented.